Catastrophic hit indicator for catcher in plunger gas/fluid lift system for well operations

ABSTRACT

A catastrophic or heavy-hit indicator subassembly is included in a plunger lift system lubricator which includes a coil spring above a striker block, a piston above the striker block, the piston sealed but moveable within the bore of the subassembly, above the piston another spring or set of spring washers, a space, and above the space a thin membrane or wall in a top nut or seal at the top of the lubricator. If the plunger reaches the lubricator with sufficient force, it will compress the coil spring and move the striker block to push the piston upward within the bore of the lubricator, the piston will compress the second spring or set of spring washers, and the top end of the piston, which is preferably pointed, will pierce the membrane or wall in the top of the lubricator.

BACKGROUND OF THE INVENTION

Producing oil and gas wells sometimes produce water as well as hydrocarbons from formation. If the height of the produced water column in the wellbore is sufficient, it will exert pressure on the formation which can exceed the formation's pressure, and thus inhibit further production. To overcome this, the water is sometimes removed from the well by a plunger lift system. A plunger deployed in the well's bore drops to near bottom hole into the water column, where it forms a piston between the formation's production pressure below and the water above. Gas produced below the plunger forces it and the water above it toward the surface, where the water can be removed and the pressure on the formation from the water column can be reduced. This function is performed cyclically, typically without intervention by the operator.

The plunger may develop quite a bit of velocity in its upward travel, so in most plunger lift systems, a ‘catcher’ is deployed in the lubricator at the top of the well's casing above surface. These lubricator/catchers are used to seal the top of the well's bore from atmosphere so that produced hydrocarbons and water can be collected from the casing below the catcher, and can provide both access to the wellbore, and a means for capturing the plunger at the upper end of its stroke where it can be removed for inspection, repair or replacement.

The lubricator/catcher may be provided with a spring or shock absorber system as well as a plunger-capture system, to protect the wellbore's sealed top from damage from by a hard hit from the plunger. Hard hits by a plunger can cause damage to the well's casing, surface equipment and/or the plunger itself. Since the well is unattended in operation, generally, such damage may not be obvious or immediately apparent.

SUMMARY OF THE INVENTION

In this invention, a component is added to a typical lubricator which includes a coil spring above a striker block, a piston above the striker block, the piston sealed but moveable within the bore of the lubricator, above the piston another spring or set of spring washers, a space, and above the space a thin membrane or wall in a top nut or seal at the top of the lubricator. If the plunger reaches the lubricator's top end with sufficient force, it will compress the coil spring and move the striker block to push the piston upward within the bore of the lubricator, the piston will compress the second spring or set of spring washers, and the top end of the piston, which is preferably pointed, will pierce the membrane or wall in the top of the lubricator. The lubricator will remained sealed because the piston is sealed within the bore of the subassembly within the lubricator, but the top nut or seal will be pierced, providing an obvious, externally observable, indication of the fact that at least one “heavy hit” has been made by the plunger to the lubricator and top-hole equipment. The spring compression forces can be designed so that the indication provided is indicative of forces which have exceeded a predetermined level of force. In this way, preventive or repair maintenance can be done by the operator prior to the plunger system failing due to absorption of too many heavy hits, or too much force from the plunger. The types of failure that heavy hits from plungers can cause include (but are not limited to) stretching of threaded components which weakens their strength and effectiveness as seals, or degradation of sealing elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway drawing of the striker block, coil spring and piston/cylinder/cap of the invention.

FIG. 2 is an exploded view of the striker block, coil spring, spring housing, piston, Belleville disc springs, and cap of the invention

FIG. 3 is a cross-sectional view of a lubricator assembly showing the placement of the subassembly of the invention at the top end of the lubricator.

FIGS. 4a and 4b are, respectively, a side elevation and a cross-sectional depiction of the elements shown in FIG. 1.

A parts list with numerical indicators is also shown, which numerals are indicated on each of the figures.

DETAILED DESCRIPTION

This invention provides a catastrophic or heavy-hit indicator subassembly for a lubricator in a plunger-lift system for oil and gas production wells.

The lubricator shown in FIG. 3 in its entirety, is provided with a heavy hit indicator subassembly, shown in FIG. 1, to be assembled within a mating cavity formed at the top of the lubricator, the cavity in communication with the bore of the lubricator and the well's bore, permitting a plunger of the lift system to enter the cavity if sufficient force is applied to the plunger in the lift system.

In an embodiment, the subassembly comprises a striker block 5 at the bottom end of a compression spring 8 which may be a coil spring, the compression spring 8 surrounding a hit indicator spring housing 1. The housing 1 is surrounded by the upper end of the coil spring 8, and the housing 1 includes in its inner part a cylinder 1 a. The cylinder is open at its top and its bottom ends. The cylinder 1 has a bottom opening which is large enough to permit the lower end of a piston 3 to pass through the opening, which may be sealed by positioning an elastic o-ring 6 between the piston's lower end extention 3 a and the housing 1 cylinder's bottom opening.

Midway along the piston 3 is a feature which provides a stop 3 b, above which the piston's upper end 3 c continues as a smaller-diameter cylinder, on which a number of Belleville washer springs 4 are stacked. Above the washers 4, and surrounding the upper tip of the piston, which may be pointed, a cap 2 is provided, attached with a seal 7 to the housing 1 at its upper end (the housing 1). The cap 2 is visible to an observer from outside of the lubricator through a port in the upper portion of the lubricator assembly (#).

When a plunger of they lift system is forced with sufficient energy to strike the lubricator and the heavy hit subassembly, the following will occur.

The plunger strikes the striker block 5, pushing it upward within the lubricator, compressing coil spring 8 and moving a sufficient distance and with sufficient force, the striker block 5 will in turn strike the lower end of the piston 3 a and force it upwards within the cylinder 1 a to compress the Belleville spring discs 4, and if sufficient force is supplied by the plunger to the subassembly, the Belleville spring discs 4 will compress sufficiently that the pointed end of the piston 3 c will pierce the indicator cap 3.

When the indicator cap 3 is pierced, it will be deformed such that an observer from outside of the lubricator can see that there has been a heavy hit, and can determine that the lubricator and top-hole equipment may require servicing or inspection.

The springs may be chosen to have characteristics such as a particular designed force to compress, to tailor the subassembly to indicate hits of specific characteristics (such as minimum force required to deform the cap).

In the preceding description, for purposes of explanation, numerous details are set out in order to provide a thorough understanding of the embodiments of the invention and how it is meant to work. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the invention as claimed. The above descriptions are intended to be examples only. Alterations, modifications, and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined by the claims of the patent flowing from the specification. 

What is claimed is:
 1. A lubricator subassembly for a plunger gas lift system for a well, the subassembly comprising: a. a striker block b. a coil spring resting on the upper end of the striker block c. a housing resting within the upper end of the coil spring d. a piston extending in a cylinder deposed through the housing e. the piston with a feature midway its length upon which a spring assembly sits f. an indicator cap above the housing capable of being pierced by the piston's upper end g. the subassembly being sealed within a chamber in the upper end of the lubricator h. the lubricator with a viewing port or window through which an observer can observe whether the indicator cap has been pierced.
 2. A method of providing an observable indication that a force above a certain magnitude has been applied to the lubricator and associated top-hole equipment and to the plunger by installing the subassembly of claim 1 with springs configured to permit the piston to pierce the indicator cap when that force has been applied by the system's plunger.
 3. The subassembly where the indicator cap is brass.
 4. The subassembly where the spring assembly is a series of Belleville spring washers or discs.
 5. The piston and cylinder housing where the piston is sealed to the cylinder by an o-ring deployed between them at the bottom of the cylinder where the piston extends out from the bottom of the cylinder.
 6. The subassembly where the housing is sealed to the lubricator by a compression seal or o-ring between the top of the housing and the indicator cap and another between the indicator cap and the top of the lubricator cavity within which the subassembly resides when installed. 